footing foundation concrete covering exposed to earth 75 mm min 1

[121974don]

Hi any thoughts on allowing maximum tolerance more than 75mm for footing foundation concrete covering? As ACI 318 is indicating Min. 75 mm.
The area of casting in place is in saudi arabia.

The contractor is proposing 100 mm ....neglecting the Change order, would you allow?

 

[SlideRuleEra]

Increased cover can mean wider cracks leading to rebar. However, 100 mm cover is probably not excessive. The US Federal Highway Administration recommends: "The minimum concrete cover for reinforcing steel embedded in concrete with direct exposure to saltwater is 100 mm (4 in); it is 75 mm (3 in) for concrete cast against earth."

Even though you are probably not dealing with saltwater, if the Contractor has a good, explainable reason, I would let him proceed.

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[121974don]

Thanks for sharing thoughts SlideRuleEra...

 

[TXStructural]

The cracks at the surface may be wider in thinner members (not always the case), but the crack width at the reinforcement will be the same, under the same forces. More cover is ALWAYS acceptable as long as it is added concrete rather than reduction of structural depth or compromise of member strength. ACI 301/318 covers are actually "specified cover" with a tolerance where you can have a limited reduction in cover and "unlimited more". The only upper limit on cover is how the cover will behave as an unreinforced concrete mass (mostly under temp and shrinkage forces.) This usually shouldn't be a concern with foundation elements.